handle additional broken pdf files in the common crawl set

- a file contained 2 indices pointing to '.notdef' for the character name so
we just take the first rather than requiring a single
- a file contained '/' (empty name) as the subtype declaration, so we fall back
to trying type 1 and truetype parsing in this situation

src/UglyToad.PdfPig.Fonts/CompactFontFormat/Charsets/CompactFontFormatCharset.cs

@@ -32,7 +32,7 @@
 
         public virtual string GetNameByStringId(int stringId)
         {
-            return GlyphIdToStringIdAndName.SingleOrDefault(x => x.Value.stringId == stringId).Value.name;
+            return GlyphIdToStringIdAndName.FirstOrDefault(x => x.Value.stringId == stringId).Value.name;
         }
 
         public virtual int GetStringIdByGlyphId(int glyphId)

src/UglyToad.PdfPig/PdfFonts/FontFactory.cs

@@ -44,6 +44,25 @@
                 return handler.Generate(dictionary);
             }
 
+            // Try simple font recovery:
+            NameToken[] orderedFallbacks = [NameToken.Type1, NameToken.TrueType];
+            foreach (var fallback in orderedFallbacks)
+            {
+                if (!handlers.TryGetValue(fallback, out handler))
+                {
+                    continue;
+                }
+
+                try
+                {
+                    return handler.Generate(dictionary);
+                }
+                catch (Exception ex)
+                {
+                    log?.Error($"Tried to parse font as fallback type: {fallback}", ex);
+                }
+            }
+
             throw new NotImplementedException($"Parsing not implemented for fonts of type: {subtype}, please submit a pull request or an issue.");
         }
     }